Fix popup menu position on non-primary displays in wxGTK

If the popup menu position was explicitly specified, it wasn't taken
into account correctly in wxGTK code as it always clamped it to the
primary display boundaries, even if the window showing the menu wasn't
on this monitor at all, typically resulting in the menu shown at the
left or right edge of the monitor instead of the correct position.

Fix this by using the display containing the window instead. This
requires passing the window, or rather the menu from which it can be
retrieved, to wxPopupMenuPositionCallback too, so add a helper struct to
pass both the position and the menu to it.

Closes https://github.com/wxWidgets/wxWidgets/pull/1621

src/gtk/window.cpp

@@ -26,6 +26,7 @@
     #include "wx/math.h"
 #endif
 
+#include "wx/display.h"
 #include "wx/dnd.h"
 #include "wx/tooltip.h"
 #include "wx/caret.h"
@@ -5678,6 +5679,12 @@ void wxWindowGTK::GTKFindWindow(GtkWidget* widget, wxArrayGdkWindows& windows)
 
 #if wxUSE_MENUS_NATIVE
 
+struct wxPopupMenuPositionCallbackData
+{
+    wxPoint pos;
+    wxMenu *menu;
+};
+
 extern "C" {
 static
 void wxPopupMenuPositionCallback( GtkMenu *menu,
@@ -5685,7 +5692,7 @@ void wxPopupMenuPositionCallback( GtkMenu *menu,
                                   gboolean * WXUNUSED(whatever),
                                   gpointer user_data )
 {
-    // ensure that the menu appears entirely on screen
+    // ensure that the menu appears entirely on the same display as the window
     GtkRequisition req;
 #ifdef __WXGTK3__
     gtk_widget_get_preferred_size(GTK_WIDGET(menu), &req, NULL);
@@ -5693,14 +5700,24 @@ void wxPopupMenuPositionCallback( GtkMenu *menu,
     gtk_widget_get_child_requisition(GTK_WIDGET(menu), &req);
 #endif
 
-    wxSize sizeScreen = wxGetDisplaySize();
+    const wxPopupMenuPositionCallbackData&
-    wxPoint *pos = (wxPoint*)user_data;
+        data = *static_cast<wxPopupMenuPositionCallbackData*>(user_data);
 
-    gint xmax = sizeScreen.x - req.width,
+    const wxRect
-         ymax = sizeScreen.y - req.height;
+        rect = wxDisplay(data.menu->GetInvokingWindow()).GetClientArea();
 
-    *x = pos->x < xmax ? pos->x : xmax;
+    wxPoint pos = data.pos;
-    *y = pos->y < ymax ? pos->y : ymax;
+    if ( pos.x < rect.x )
+        pos.x = rect.x;
+    if ( pos.y < rect.y )
+        pos.y = rect.y;
+    if ( pos.x + req.width > rect.GetRight() )
+        pos.x = rect.GetRight() - req.width;
+    if ( pos.y + req.height > rect.GetBottom() )
+        pos.y = rect.GetBottom() - req.height;
+
+    *x = pos.x;
+    *y = pos.y;
 }
 }
 
@@ -5708,7 +5725,7 @@ bool wxWindowGTK::DoPopupMenu( wxMenu *menu, int x, int y )
 {
     wxCHECK_MSG( m_widget != NULL, false, wxT("invalid window") );
 
-    wxPoint pos;
+    wxPopupMenuPositionCallbackData data;
     gpointer userdata;
     GtkMenuPositionFunc posfunc;
     if ( x == -1 && y == -1 )
@@ -5719,8 +5736,9 @@ bool wxWindowGTK::DoPopupMenu( wxMenu *menu, int x, int y )
     }
     else
     {
-        pos = ClientToScreen(wxPoint(x, y));
+        data.pos = ClientToScreen(wxPoint(x, y));
-        userdata = &pos;
+        data.menu = menu;
+        userdata = &data;
         posfunc = wxPopupMenuPositionCallback;
     }